Over-the-top (OTT) platforms are digital service providers that deliver streaming media content, such as movies, TV series, music, and other forms of media, directly to consumers through internet connectivity, thereby bypassing traditional broadcast distribution systems such as terrestrial, satellite, or cable television networks ^[1][2][1,2]. These platforms leverage Internet Protocol (IP) technology to transmit content, functioning similarly to Internet Protocol Television (IPTV) but usually providing services at higher standards [1]. While such platforms generally use ad-based video on demand, subscription-based video on demand (SVOD), transactional video on demand, and hybrid business models [3], some well-known OTT services are Netflix, Hulu, Disney+, and Amazon Prime.

OTT platforms offer numerous benefits, such as convenient access to video content anytime and anywhere, a wide variety of content options, personalized recommendations, flexible viewing hours, multi-device support, and additional advantages through subscription plans. Therefore, OTT platforms are significantly transforming traditional television viewing habits and gaining acceptance as the “new television” in society [4], with OTT services playing a central role in driving changes in video content consumption patterns [5].

The lockdowns caused by COVID-19 have considerably increased the adoption of OTT platforms, resulting in an increase in usage and a rise in subscribers. The global consumer base for OTT services is anticipated to reach approximately 4.22 billion users by 2027, with a penetration rate of 53%. In addition, the revenue generated by OTT platforms is projected to reach EUR 277 billion in 2023 [6]. Improving usability becomes crucial to maintaining customer satisfaction and fostering brand loyalty in these rapidly expanding systems.

Usability is defined as a quality feature evaluating the ease of use of user interfaces and is described with five quality components: learnability, efficiency, memorability, errors, and satisfaction [7]. The ISO defines usability as the “extent to which a system, product, or service can be used by specified users to achieve specified goals with effectiveness, efficiency, and satisfaction in a specified context of use” [8]. Usability is a broader concept than ease of use and user-friendliness; it refers to the effective, efficient, and satisfactory interaction with a system, product, or service, considering diverse user capabilities across all system interactions, including learning, regular, or infrequent use [9]. Furthermore, integrating usability principles at various stages of the design, development, and evaluation process enhances the quality and acceptance of a new system ^[7][10][7,10]. By considering usability factors early on, developers can address potential issues, resulting in a user-friendly and efficient system. This approach minimizes the need for later modifications, leading to effective and user-centric systems that improve the overall user experience, satisfaction, and brand loyalty [11].

In the literature, there are several studies investigating the factors affecting the adoption of OTT platforms or streaming services (e.g., ^{[12][13][14][15][16][17][18]}[37,38,39,40,41,42,43]). Furthermore, Mulla [3] reviewed the literature to determine the factors influencing the adoption of OTT platforms. The results show that content, price, flexibility, convenience (perceived ease of use), perceived usefulness, perceived enjoyment (hedonic motivation), desire to be freed from any constraint, entertainment value, socialization, culture inclusion, binge-watching, and self-efficacy are the critical factors for OTT adoption. On the other hand, in the literature, there is a limited number of studies regarding the usability of OTT platforms. These studies are not specifically OTT-focused and generally concentrate on the usability of specific applications that provide video streaming services. Krishnan and Sitaraman ^[19][12] conducted an in-depth investigation and found that video streaming quality, especially factors like startup delay, significantly impacts viewer behavior. Hussain et al. ^[20][13] identified video streaming and its quality as dominant usability metrics for mobile apps. Hussain et al. ^[21][14] assessed YouTube’s usability using video recordings, heatmaps, and questionnaires to evaluate metrics like ease of use and satisfaction. Eliseo et al. ^[22][15] provided interface guidelines for OTT platforms like Netflix using Nielsen’s heuristics. Yang et al. ^[23][16] assessed the usability of multiple SVOD services, such as Netflix, Amazon Prime, and Hulu, by conducting questionnaires. Kollmorgen et al. ^[24][17] highlighted Netflix’s higher UX ratings across several questionnaires, including the UEQ (User Experience Questionnaire), SUS (System Usability Scale), and UMUX (Usability Metric for User Experience). These studies on video streaming and OTT platforms ^{[19][20][21][22][23][24]}[12,13,14,15,16,17] evaluated the usability of OTT platforms using various usability evaluation methods, including usability tests, heuristic evaluation, and questionnaires. However, none of them attempted to develop a dedicated instrument for evaluating the usability of OTT platforms. Several studies have conducted user tests on TVs and related systems. For instance, Obrist et al. ^[25][20] utilized eye tracking to study usability challenges for users above 50 years of age with interactive TV applications. Bernhaupt et al. ^[26][18] employed a combination of field studies, heuristic evaluations, and user testing to uncover usability challenges associated with iTV, a UK-based free television channel. Lim et al. ^[27][24] assessed the usability of smart TV interfaces and remotes with diverse age groups. The research by Miesler et al. ^[28][26] and Lee and Shin ^[29][44] examined user experience and interface comparisons of smart TVs, respectively. Dou et al. ^[30][28] and Ouyang and Zhou ^[31][27] both focused on usability problems faced by older people in China when using smart TVs. Awale and Murano ^[32][30] evaluated the Apple TV interface against Nielsen’s heuristics, while Bures et al. ^[33][31] introduced an automated model-based approach for usability testing. Gumussoy et al. ^[34][33] conducted a usability test using the concurrent think-aloud method, surveys, eye tracking, expression analysis, and logging techniques, investigating the relationships between usability metrics in TV-related studies. In the studies that conducted user tests for TV and similar systems ^{[25][26][27][28][30][31][33][34]}[18,20,24,26,27,28,31,33], specific usability problems related to the tested system were identified. However, these studies did not propose any general principles for the design of TV systems. On the other hand, several studies in the literature suggest principles, heuristics (general usability principles), and checklists to analyze and improve the usability of TV-related services ^{[35][36][37][38][39][40][41][42][43]}[19,21,23,25,29,32,34,35,36]. Kim et al. ^[35][19] identified 21 usability principles for personalized electronic program guides for digital TVs, such as controllability, feedback, error, predictability, learnability, memorability, and consistency. Chorianopoulos ^[41][34] proposed user interface design principles for interactive TVs, such as viewer as a director, participatory content authoring, diverse content sources, and infotainment. Then, the principles were applied to redesign music TV as an iTV application. Geerts and De Grooff ^[36][21] conducted user testing on social TVs, identifying participant issues during testing and converting these issues into sociability guidelines, including personal privacy and group privacy, sharing content flexibly, and minimizing distraction from TV programs. Collazos et al. ^[42][35] adapted Nielsen’s ten heuristics to suit the design of an interactive digital television (iDT), incorporating additional heuristics related to navigation, information structure, physical constraints, and considerations for extraordinary users. Solano et al. ^[37][23] defined a refined set of usability heuristics proposed by Collazos et al. ^[42][35] for iDT applications. Solano et al. ^[38][25] proposed a usability checklist for iDT applications using the heuristics proposed by Solano et al. ^[37][23]. They validated the checklist’s effectiveness through expert evaluations, enabling a comparative analysis of the number and severity of usability problems against Nielsen’s heuristics. Fernandes et al. ^[43][36] introduced graphic and interaction guidelines for iTV systems using Google Material Design and Apple tvOS guides. Kaya et al. ^[40][32] proposed 16 usability heuristics and a guideline specific to set-top box and TV systems. The proposed heuristics were validated through user testing, expert judgment, and heuristic evaluation. They determined the most critical heuristics related to catastrophic usability problems to be visibility of system status, pleasurable and respectful interaction with the user, privacy, parental control, and easy access.